AlthoughinsomerespectsmoretechnicalintheirsubjectsandstylethanDarwin’s“Journal，“thebooksherereprintedwillneverlosetheirvalueandinterestfortheoriginalityoftheobservationstheycontain。Manypartsofthemareadmirablyadaptedforgivinganinsightintoproblemsregardingthestructureandchangesoftheearth’ssurface，andinfacttheyformacharmingintroductiontophysicalgeologyandphysiographyintheirapplicationtospecialdomains。Thebooksthemselvescannotbeobtainedformanytimesthepriceofthepresentvolume，andboththegeneralreader，whodesirestoknowmoreofDarwin’swork，andthestudentofgeology，whonaturallywishestoknowhowamastermindreasonedonmostimportantgeologicalsubjects，willbegladoftheopportunityofpossessingtheminaconvenientandcheapform。
Thethreeintroductions，whichmyfriendProfessorJuddhaskindlyfurnished，givecriticalandhistoricalinformationwhichmakesthiseditionofspecialvalue。
G。T。B。
TABLEOFCONTENTS。
CRITICALINTRODUCTION。
CHAPTERI——ONTHEELEVATIONOFTHEEASTERNCOASTOFSOUTHAMERICA。
UpraisedshellsofLaPlata——BahiaBlanca，Sand-dunesandPumice-pebbles——
Step-formedplainsofPatagonia，withupraisedshells——Terrace-boundedvalleyofSantaCruz，formerlyasea-strait——UpraisedshellsofTierradelFuego——Lengthandbreadthoftheelevatedarea——Equabilityofthemovements，asshownbythesimilarheightsoftheplains——Slownessoftheelevatoryprocess——Modeofformationofthestep-formedplains——Summary——
GreatshingleformationofPatagonia;itsextent，origin，anddistribution——Formationofsea-cliffs。
CHAPTERII——ONTHEELEVATIONOFTHEWESTERNCOASTOFSOUTHAMERICA。
ChonosArchipelago——Chiloe，recentandgradualelevationof，traditionsoftheinhabitantsonthissubject——Concepcion，earthquakeandelevationof——
VALPARAISO，greatelevationof，upraisedshells，earthormarineorigin，gradualriseofthelandwithinthehistoricalperiod——COQUIMBO，elevationof，inrecenttimes;terracesofmarineorigin，theirinclination，theirescarpmentsnothorizontal——Guasco，gravelterracesof——Copiapo——PERU——
UpraisedshellsofCobija，Iquique，andArica——Lima，shell-bedsandsea-
beachonSanLorenzo——Humanremains，fossilearthenware，earthquakedebacle，recentsubsidence——Onthedecayofupraisedshells——Generalsummary。
CHAPTERIII——ONTHEPLAINSANDVALLEYSOFCHILE：——SALIFEROUSSUPERFICIAL
DEPOSITS。
Basin-likeplainsofChile;theirdrainage，theirmarineorigin——Marksofsea-actionontheeasternflanksoftheCordillera——Slopingterrace-likefringesofstratifiedshinglewithinthevalleysoftheCordillera;theirmarineorigin——BouldersinthevalleyofCachapual——HorizontalelevationoftheCordillera——Formationofvalleys——Bouldersmovedbyearthquake-
waves——Salinesuperficialdeposits——BedofnitrateofsodaatIquique——
Salineincrustations——Salt-lakesofLaPlataandPatagonia;purityofthesalt;itsorigin。
CHAPTERIV——ONTHEFORMATIONSOFTHEPAMPAS。
Mineralogicalconstitution——Microscopicalstructure——BuenosAyres，shellsembeddedintosca-rock——BuenosAyrestotheColorado——S。Ventana——BahiaBlanca;M。Hermoso，bonesandinfusoriaof;P。Alta，shells，bones，andinfusoriaof;co-existenceoftherecentshellsandextinctmammifers——
BuenosAyrestoSt。Fe——SkeletonsofMastodon——Infusoria——Inferiormarinetertiarystrata，theirage——Horse’stooth。BANDAORIENTAL——
SuperficialPampeanformation——Inferiortertiarystrata，variationof，connectedwithvolcanicaction;MacraucheniaPatachonicaatS。JulianinPatagonia，ageof，subsequenttolivingmolluscaandtotheerraticblockperiod。SUMMARY——AreaofPampeanformation——Theoriesoforigin——Sourceofsediment——Estuaryorigin——Contemporaneouswithexistingmollusca——
Relationstounderlyingtertiarystrata。Ancientdepositofestuaryorigin——ElevationandsuccessivedepositionofthePampeanformation——
Numberandstateoftheremainsofmammifers;theirhabitation，food，extinction，andrange——Conclusion——SupplementonthethicknessofthePampeanformation——LocalitiesinPampasatwhichmammiferousremainshavebeenfound。
CHAPTERV——ONTHEOLDERTERTIARYFORMATIONSOFPATAGONIAANDCHILE。
RioNegro——S。Josef——PortDesire，whitepumiceousmudstonewithinfusoria——PortS。Julian——SantaCruz，basalticlavaof——P。Gallegos——
EasternTierradelFuego;leavesofextinctbeech-trees——SummaryonthePatagoniantertiaryformations——TertiaryformationsoftheWesternCoast——
ChonosandChiloegroups，volcanicrocksof——Concepcion——Navidad——
Coquimbo——Summary——Ageofthetertiaryformations——Linesofelevation——
Silicifiedwood——ComparativerangesoftheextinctandlivingmolluscaontheWestCoastofS。America——Climateofthetertiaryperiod——OnthecausesoftheabsenceofrecentconchiferousdepositsonthecoastsofSouthAmerica——Onthecontemporaneousdepositionandpreservationofsedimentaryformations。
CHAPTERVI——PLUTONICANDMETAMORPHICROCKS：——CLEAVAGEANDFOLIATION。
Brazil，Bahia，gneisswithdisjointedmetamorphoseddikes——Strikeoffoliation——RiodeJaneiro，gneiss-granite，embeddedfragmentin，decompositionof——LaPlata，metamorphicandoldvolcanicrocksof——S。
Ventana——ClaystoneporphyryformationofPatagonia;singularmetamorphicrocks;pseudo-dikes——FalklandIslands，palaeozoicfossilsof——TierradelFuego，clay-slateformation，cretaceousfossilsof;cleavageandfoliation;
formofland——ChonosArchipelago，mica-schists，foliationdisturbedbygraniticaxis;dikes——Chiloe——Concepcion，dikes，successiveformationof——CentralandNorthernChile——Concludingremarksoncleavageandfoliation——Theircloseanalogyandsimilarorigin——Stratificationofmetamorphicschists——Foliationofintrusiverocks——Relationofcleavageandfoliationtothelinesoftensionduringmetamorphosis。
CHAPTERVII——CENTRALCHILE：——STRUCTUREOFTHECORDILLERA。
CentralChile——BasalformationsoftheCordillera——Originoftheporphyriticclay-stoneconglomerate——Andesite——Volcanicrocks——SectionoftheCordillerabythePeuquenesorPortilloPass——Greatgypseousformation——Peuquenesline;thicknessofstrata，fossilsof——Portilloline——Conglomerate，orthiticgranite，mica-schist，volcanicrocksof——
ConcludingremarksonthedenudationandelevationofthePortilloline——
SectionbytheCumbre，orUspallataPass——Porphyries——Gypseousstrata——
SectionnearthePuentedelInca;fossilsof——Greatsubsidence——Intrusiveporphyries——PlainofUspallata——SectionoftheUspallatachain——
Structureandnatureofthestrata——Silicifiedverticaltrees——Greatsubsidence——Graniticrocksofaxis——ConcludingremarksontheUspallatarange;originsubsequenttothatofthemainCordillera;twoperiodsofsubsidence;comparisonwiththePortillochain。
CHAPTERVIII——NORTHERNCHILE——CONCLUSION。
SectionfromIllapeltoCombarbala;gypseousformationwithsilicifiedwood——Panuncillo——Coquimbo;minesofArqueros;sectionupvalley;
fossils——Guasco，fossilsof——Copiapo，sectionupvalley;LasAmolanas，silicifiedwood——Conglomerates，natureofformerland，fossils，thicknessofstrata，greatsubsidence——ValleyofDespoblado，fossils，tufaceousdeposit，complicateddislocationsof——Relationsbetweenancientorificesoferuptionandsubsequentaxesofinjection——Iquique，Peru，fossilsof，salt-deposits——Metalliferousveins——Summaryontheporphyriticconglomerateandgypseousformations——Greatsubsidencewithpartialelevationsduringthecretaceo-ooliticperiod——OntheelevationandstructureoftheCordillera——Recapitulationonthetertiaryseries——
Relationbetweenmovementsofsubsidenceandvolcanicaction——Pampeanformation——Recentelevatorymovements——Long-continuedvolcanicactionintheCordillera——Conclusion。
INDEX。
GEOLOGICALOBSERVATIONSONSOUTHAMERICA
BY
CHARLESDARWIN。
CRITICALINTRODUCTION。
Oftheremarkable“trilogy“constitutedbyDarwin’swritingswhichdealwiththegeologyofthe“Beagle，“thememberwhichhasperhapsattractedleastattention，uptothepresenttimeisthatwhichtreatsofthegeologyofSouthAmerica。TheactualwritingofthisbookappearstohaveoccupiedDarwinashorterperiodthaneitheroftheothervolumesoftheseries;hisdiaryrecordsthattheworkwasaccomplishedwithintenmonths，namely，betweenJuly1844andApril1845;butthebookwasnotactuallyissuedtilllateintheyearfollowing，theprefacebearingthedate“September1846。”
Altogether，asDarwininformsusinhis“Autobiography，“thegeologicalbooks“consumedfourandahalfyears’steadywork，“mostoftheremainderofthetenyearsthatelapsedbetweenthereturnofthe“Beagle，“andthecompletionofhisgeologicalbooksbeing，itissadtorelate，“lostthroughillness！”
Concerningthe“GeologicalObservationsonSouthAmerica，“DarwinwrotetohisfriendLyell，asfollows：——“Myvolumewillbeabout240pages，dreadfullydull，yetmuchcondensed。Ithinkwheneveryouhavetimetolookthroughit，youwillthinkthecollectionoffactsontheelevationofthelandandontheformationofterracesprettygood。”
“Muchcondensed“istheverdictthateveryonemustendorse，onrisingfromtheperusalofthisremarkablebook;butbynomeans“dull。”ThethreeandahalfyearsfromApril1832toSeptember1835，werespentbyDarwininSouthAmerica，andweredevotedtocontinuousscientificwork;theproblemshedealtwithwereeitherpurelygeologicalorthosewhichconstitutetheborderlandbetweenthegeologicalandbiologicalsciences。Itisimpossibletoreadthejournalwhichhekeptduringthistimewithoutbeingimpressedbytheconvictionthatitcontainsallthegermsofthoughtwhichafterwardsdevelopedintothe“OriginofSpecies。”ButitisequallyevidentthatafterhisreturntoEngland，biologicalspeculationsgraduallybegantoexerciseamoreexclusiveswayoverDarwin’smind，andtendedtodispossessgeology，whichduringtheactualperiodofthevoyagecertainlyengrossedmostofhistimeandattention。ThewonderfulseriesofobservationsmadeduringthosethreeandahalfyearsinSouthAmericacouldscarcelybedonejusticeto，inthe240pagesdevotedtotheirexposition。ThatheexecutedtheworkofpreparingthebookonSouthAmericainsomewhatthemannerofatask，isshownbymanyreferencesinhisletters。WritingtoSirJosephHookerin1845，hesays，“IhopethisnextsummertofinishmySouthAmericanGeology，thentogetoutalittleZoology，andHURRAHFORMYSPECIESWORK！”
Itwouldseemthatthefeelingofdisappointment，whichDarwinsooftenexperiencedincomparingabookwhencompleted，withtheobservationsandspeculationswhichhadinspiredit，wasmorekeenlyfeltinthecaseofhisvolumeonSouthAmericathananyother。Toonefriendhewrites，“Ihaveoflatebeenslavingextrahard，tothegreatdiscomfitureofwretcheddigestiveorgans，atSouthAmerica，andthankallthefates，Ihavedonethree-fourthsofit。WritingplainEnglishgrowswithmemoreandmoredifficult，andneverattainable。Asforyourpretendingthatyouwillreadanythingsodullasmypuregeologicaldescriptions，laynotsuchaflatteringunctiononmysoul，foritisincredible。”Toanotherfriendhewrites，“Youdonotknowwhatyouthreatenwhenyouproposetoreadit——itispurelygeological。Isaidtomybrother，’Youwillofcoursereadit，’
andhisanswerwas，’Uponmylife，Iwouldsoonerevenbuyit。’“
Inspiteofthesedisparagingremarks，however，wearestronglyinclinedtobelievethatthisbook，despisedbyitsauthor，andneglectedbyhiscontemporaries，willintheendbeadmittedtobeoneofDarwin’schieftitlestofame。Itis，perhaps，anunfortunatecircumstancethatthegreatsuccesswhichheattainedinbiologybythepublicationofthe“OriginofSpecies“has，tosomeextent，overshadowedthefactthatDarwin’sclaimsasageologist，areoftheveryhighestorder。Itisnottoomuchtosaythat，hadDarwinnotbeenageologist，the“OriginofSpecies“couldneverhavebeenwrittenbyhim。Butapartfromthosegeologicalquestions，whichhaveanimportantbearingonbiologicalthoughtandspeculation，suchastheproofsofimperfectioninthegeologicalrecord，therelationsofthelatertertiaryfaunastotherecentonesinthesameareas，andtheapparentinterminglingoftypesbelongingtodistantgeologicalepochs，whenwestudythepalaeontologyofremotedistricts，——thereareotherpurelygeologicalproblems，uponwhichthecontributionsmadebyDarwinareoftheveryhighestvalue。IbelievethattheverdictofthehistoriansofsciencewillbethatifDarwinhadnottakenaforemostplaceamongthebiologistsofthiscentury，hispositionasageologistwouldhavebeenanalmostequallycommandingone。
ButinthecaseofDarwin’sprincipalgeologicalwork——thatrelatingtotheoriginofthecrystallineschists，——geologistswerenotatthetimepreparedtoreceivehisrevolutionaryteachings。Theinfluenceofpowerfulauthoritywaslongexercised，indeed，tostiflehisteaching，andonlynow，whenthisunfortunateoppositionhasdisappeared，isthetruenatureandimportanceofDarwin’spurelygeologicalworkbeginningtoberecognised。
Thetwofirstchaptersofthe“GeologicalObservationsonSouthAmerica，“
dealwiththeproofswhichexistofgreat，butfrequentlyinterrupted，movementsofelevationduringveryrecentgeologicaltimes。Inconnectionwiththissubject，Darwin’sparticularattentionwasdirectedtotherelationsbetweenthegreatearthquakesofSouthAmerica——ofsomeofwhichhehadimpressiveexperience——andthepermanentchangesofelevationwhichweretakingplace。Hewasmuchstruckbytherapiditywithwhichtheevidenceofsuchgreatearthmovementsisfrequentlyobliterated;andespeciallywiththeremarkablewayinwhichtheactionofrain-water，percolatingthroughdepositsontheearth’ssurface，removesalltracesofshellsandothercalcareousorganisms。Itwastheseconsiderationswhichweretheparentsofthegeneralisationthatapalaeontologicalrecordcanonlybepreservedduringthoseperiodsinwhichlong-continuedslowsubsidenceisgoingon。Thisinturn，ledtothestillwiderandmoresuggestiveconclusionthatthegeologicalrecordasawholeis，andnevercanbemorethan，aseriesofmoreorlessisolatedfragments。Therecognitionofthisimportantfactconstitutesthekeystonetoanytheoryofevolutionwhichseekstofindabasisintheactualstudyofthetypesoflifethathaveformerlyinhabitedourglobe。
Inhisthirdchapter，Darwingivesanumberofinterestingfacts，collectedduringhisvisitstotheplainsandvalleysofChili，whichbearonthequestionoftheoriginofsaliferousdeposits——theaccumulationofsalt，gypsum，andnitrateofsoda。Thisisaproblemthathasexcitedmuchdiscussionamonggeologists，andwhich，inspiteofmanyvaluableobservations，stillremainstoagreatextentveryobscure。AmongtheimportantconsiderationsinsisteduponbyDarwinisthatrelatingtotheabsenceofmarineshellsinbedsassociatedwithsuchdeposits。Hejustlyarguesthatifthestratawereformedinshallowwaters，andthenexposedbyupheavaltosubaerialaction，allshellsandothercalcareousorganismswouldberemovedbysolution。
FollowingLyell’smethod，Darwinproceedsfromthestudyofdepositsnowbeingaccumulatedontheearth’ssurface，tothosewhichhavebeenformedduringthemorerecentperiodsofthegeologicalhistory。
HisaccountofthegreatPampeanformation，withitswonderfulmammalianremains——Mastodon，Toxodon，Scelidotherium，Macrauchenia，Megatherium，Megalonyx，Mylodon，andGlyptodon——thisfullofinterest。HisdiscoveryoftheremainsofatrueEquusaffordedaremarkableconfirmationofthefact——
alreadymadeoutinNorthAmerica——thatspeciesofhorsehadexistedandbecomeextinctintheNewWorld，beforetheirintroductionbytheSpaniardsinthesixteenthcentury。FullyperceivingtheimportanceofthemicroscopeinstudyingthenatureandoriginofsuchdepositsasthoseofthePampas，DarwinsubmittedmanyofhisspecimensbothtoDr。Carpenterinthiscountry，andtoProfessorEhrenberginBerlin。Manyveryimportantnotesonthemicroscopicorganismscontainedintheformationwillbefoundscatteredthroughthechapter。
Darwin’sstudyoftheoldertertiaryformations，withtheirabundantshells，andtheirrelicsofvegetablelifeburiedundergreatsheetsofbasalt，ledhimtoconsidercarefullythequestionofclimateduringtheseearlierperiods。Inoppositiontoprevalentviewsonthissubject，Darwinpointsoutthathisobservationsareopposedtotheconclusionthatahighertemperatureprevaileduniversallyovertheglobeduringearlygeologicalperiods。Hearguesthat“thecauseswhichgavetotheoldertertiaryproductionsofthequitetemperatezonesofEuropeatropicalcharacter，WEREOFALOCALCHARACTERANDDIDNOTAFFECTTHEWHOLEGLOBE。”
Inthis，asinmanysimilarinstances，weseethebeneficialinfluenceofextensivetravelinfreeingDarwin’smindfromprevailingprejudices。Itwasthiswideningofexperiencewhichrenderedhimsoespeciallyqualifiedtodealwiththegreatproblemoftheoriginofspecies，andindoingsotoemancipatehimselffromideaswhichwerereceivedwithunquestioningfaithbygeologistswhosestudieshadbeencircumscribedwithinthelimitsofWesternEurope。
IntheCordillerasofNorthernandCentralChili，Darwin，whenstudyingstillolderformations，clearlyrecognisedthattheycontainanadmixtureoftheformsoflife，whichinEuropearedistinctiveoftheCretaceousandJurassicperiodsrespectively。Hewasthusledtoconcludethattheclassificationofgeologicalperiods，whichfairlywellexpressesthefactsthathadbeendiscoveredintheareaswherethesciencewasfirststudied，isnolongercapableofbeingappliedwhenwecometothestudyofwidelydistantregions。Thisimportantconclusionleduptothefurthergeneralisationthateachgreatgeologicalperiodhasexhibitedageographicaldistributionoftheformsofanimalandvegetablelife，comparabletothatwhichprevailsintheexistingfaunaandflora。Tothosewhoarefamiliarwiththeextenttowhichthedoctrineofuniversalformationshasaffectedgeologicalthoughtandspeculation，bothlongbeforeandsincethetimethatDarwinwrote，theimportanceofthisnewstandpointtowhichhewasabletoattainwillbesufficientlyapparent。
LiketheideaoftheextremeimperfectionoftheGeologicalRecord，thedoctrineofLOCALgeologicalformationsisfoundpermeatingandmouldingallthepalaeontologicalreasoningsofhisgreatwork。
InoneofDarwin’sletters，writtenwhilehewasinSouthAmerica，thereisapassagewehavealreadyquoted，inwhichheexpresseshisinabilitytodecidebetweentherivalclaimsuponhisattentionof“theoldcrystallinegroupofrocks，“and“thesofterfossiliferousbeds“respectively。Thesixthchapteroftheworkbeforeus，entitled“PlutonicandMetamorphicRocks——CleavageandFoliation，“containsabriefsummaryofaseriesofobservationsandreasoningsuponthesecrystallinerocks，whichare，webelieve，calculatedtoeffectarevolutioningeologicalscience，and——
thoughtheirvalueandimportancehavelongbeenoverlooked——arelikelytoentitleDarwininthefuturetoapositionamonggeologists，scarcely，ifatall，inferiortothatwhichhealreadyoccupiesamongbiologists。
Darwin’sstudiesofthegreatrock-massesoftheAndesconvincedhimofthecloserelationsbetweenthegraniticorPlutonicrocks，andthosewhichwereundoubtedlypouredforthaslavas。Uponhisreturn，hesettowork，withtheaidofProfessorMiller，tomakeacarefulstudyofthemineralscomposingthegranitesandthosewhichoccurinthelavas，andhewasabletoshowthatinallessentialrespectstheyareidentical。Hewasfurtherabletoprovethatthereisacompletegradationbetweenthehighlycrystallineorgraniticrock-masses，andthosecontainingmoreorlessglassymatterbetweentheircrystals，whichconstituteordinarylavas。Theimportanceofthisconclusionwillberealisedwhenwerememberthatitwasthenthecommoncreedofgeologists——andstillcontinuestobesoontheContinent——thatallhighlycrystallinerocksareofgreatgeologicalantiquity，andthattheigneousejectionswhichhavetakenplacesincethebeginningofthetertiaryperiodsdifferessentially，intheircomposition，theirstructure，andtheirmodeofoccurrence，fromthosewhichhavemadetheirappearanceatearlierperiodsoftheworld’shistory。
VerycompletelyhavetheconclusionsofDarwinuponthesesubjectsbeenjustifiedbyrecentresearches。InEngland，theUnitedStates，andItaly，examplesofthegradualpassageofrocksoftrulygraniticstructureintoordinarylavashavebeendescribed，andtherealityofthetransitionhasbeendemonstratedbythemostcarefulstudieswiththemicroscope。RecentresearchescarriedoninSouthAmericabyProfessorStelzner，havealsoshowntheexistenceofaclassofhighlycrystallinerocks——the“Andengranites“——whichcombineinthemselvesmanyofthecharacteristicswhichwereoncethoughttobedistinctiveoftheso-calledPlutonicandvolcanicrocks。Noonefamiliarwithrecentgeologicalliterature——eveninGermanyandFrance，wheretheoldviewsconcerningthedistinctionofigneousproductsofdifferentageshavebeenmoststoutlymaintained——canfailtorecognisethefactthattheprinciplescontendedforbyDarwinbidfairatnodistantperiodtowinuniversalacceptanceamonggeologistsallovertheglobe。
StillmoreimportantaretheconclusionsatwhichDarwinarrivedwithrespecttotheoriginoftheschistsandgneisseswhichcoversolargeanareainSouthAmerica。
Carefullynoting，bytheaidofhiscompassandclinometer，ateverypointwhichhevisited，thedirectionandamountofinclinationoftheparalleldivisionsintheserocks，hewasledtoaveryimportantgeneralisation——
namely，thatoververywideareasthedirection(strike)oftheplanesofcleavageinslates，andoffoliationinschistsandgneisses，remainedconstant，thoughtheamountoftheirinclination(dip)oftenvariedwithinwidelimits。Furtherthanthisitappearedthattherewasalwaysaclosecorrespondencebetweenthestrikeofthecleavageandfoliationandthedirectionofthegreataxesalongwhichelevationhadtakenplaceinthedistrict。
InTierradelFuego，Darwinfoundstrikingevidencethatthecleavageintersectinggreatmassesofslate-rockswasquiteindependentoftheiroriginalstratification，andcouldoften，indeed，beseencuttingacrossitatrightangles。HewasalsoabletoverifySedgwick’sobservationthat，insomeslates，glossysurfacesontheplanesofcleavagearisefromthedevelopmentofnewminerals，chlorite，epidoteormica，andthatinthiswayacompletegraduationfromslatestotrueschistsmaybetraced。
Darwinfurthershowedthatinhighlyschistoserocks，thefoliabendaroundandencircleanyforeignbodiesinthemass，andthatinsomecasestheyexhibitthemosttortuousformsandcomplicatedpuckerings。Heclearlysawthatinallcasestheforcesbywhichthesestrikingphenomenamusthavebeenproducedwerepersistentoverwideareas，andwereconnectedwiththegreatmovementsbywhichtherockshadbeenupheavedandfolded。
Thatthedistinctfoliaofquartz，feldspar，mica，andothermineralscomposingthemetamorphicschistscouldnothavebeenseparatelydepositedassedimentwasstronglyinsisteduponbyDarwin;andindoingsoheopposedtheviewgenerallyprevalentamonggeologistsatthattime。Hewasthusdriventotheconclusionthatfoliation，likecleavage，isnotanoriginal，butasuperinducedstructureinrock-masses，andthatitistheresultofre-crystallisation，underthecontrollinginfluenceofgreatpressure，ofthematerialsofwhichtherockwascomposed。
InstudyingthelavasofAscension，aswehavealreadyseen，Darwinwasledtorecognisethecircumstancethat，whenigneousrocksaresubjectedtogreatdifferentialmovementsduringtheperiodoftheirconsolidation，theyacquireafoliatedstructure，closelyanalogoustothatofthecrystallineschists。Likehispredecessorinthisfieldofinquiry，Mr。PoulettScrope，CharlesDarwinseemstohavebeengreatlyimpressedbythesefacts，andhearguedfromthemthattherocksexhibitingthefoliatedstructuremusthavebeeninastateofplasticity，likethatofacoolingmassoflava。AtthattimethesuggestiveexperimentsofTresca，Daubree，andothers，showingthatsolidmassesundertheinfluenceofenormouspressurebecomeactuallyplastic，hadnotbeenpublished。HadDarwinbeenawareofthesefactshewouldhaveseenthatitwasnotnecessarytoassumeastateofimperfectsolidityinrock-massesinordertoaccountfortheirhavingyieldedtopressureandtension，and，indoingso，acquiringthenewcharacterswhichdistinguishthecrystallineschists。
TheviewsputforwardbyDarwinontheoriginofthecrystallineschistsfoundanableadvocateinMr。DanielSharpe，whoin1852and1854publishedtwopapers，dealingwiththegeologyoftheScottishHighlandsandoftheAlpsrespectively，inwhichheshowedthattheprinciplesarrivedatbyDarwinwhenstudyingtheSouthAmericanrocksaffordacompleteexplanationofthestructureofthetwodistrictsinquestion。
But，ontheotherhand，theconclusionsofDarwinandSharpeweremetwiththestrongestoppositionbySirRoderickMurchisonandDr。A。Geikie，whoin1861readapaperbeforetheGeologicalSociety“OntheCoincidencebetweenStratificationandFoliationintheCrystallineRocksoftheScottishHighlands，“inwhichtheyinsistedthattheirobservationsinScotlandtendedtoentirelydisprovetheconclusionsofDarwinthatfoliationinrocksisasecondarystructure，andentirelyindependentoftheoriginalstratificationoftherock-masses。
Nowitisamostsignificantcircumstancethat，nosoonerdidtheofficersoftheGeologicalSurveycommencethecarefulanddetailedstudyoftheScottishHighlandsthantheyfoundthemselvescompelledtomakeaformalretractionoftheviewswhichhadbeenputforwardbyMurchisonandGeikieinoppositiontotheconclusionsofDarwin。TheofficersoftheGeologicalSurveyhavecompletelyabandonedtheviewthatthefoliationoftheHighlandrockshasbeendeterminedbytheiroriginalstratification，andadmitthatthestructureistheresultoftheprofoundmovementstowhichtherockshavebeensubjected。Thesameconclusionshaverecentlybeensupportedbyobservationsmadeinmanydifferentdistricts——amongwhichwemayespeciallyrefertothoseofDr。H。ReuschinNorway，andthoseofDr。
J。LehmanninSaxony。AtthepresenttimetheargumentssoclearlystatedbyDarwinintheworkbeforeus，have，afterenduringoppositionorneglectforawholegeneration，begunto“triumphallalongtheline，“andwemaylookforwardconfidentlytothenearfuture，whenhisclaimtoberegardedasoneofthegreatestofgeologicaldiscoverersshallbefullyvindicated。
JOHNW。JUDD。
CHAPTERI。ONTHEELEVATIONOFTHEEASTERNCOASTOFSOUTHAMERICA。
UpraisedshellsofLaPlata。
BahiaBlanca，Sand-dunesandPumice-pebbles。
Step-formedplainsofPatagonia，withupraisedShells。
Terrace-boundedValleyofSantaCruz，formerlyaSea-strait。
UpraisedshellsofTierradelFuego。
Lengthandbreadthoftheelevatedarea。
Equabilityofthemovements，asshownbythesimilarheightsoftheplains。
Slownessoftheelevatoryprocess。
Modeofformationofthestep-formedplains。
Summary。
GreatShingleFormationofPatagonia;itsextent，origin，anddistribution。
Formationofsea-cliffs。
InthefollowingVolume，whichtreatsofthegeologyofSouthAmerica，andalmostexclusivelyofthepartssouthwardoftheTropicofCapricorn，I
havearrangedthechaptersaccordingtotheageofthedeposits，occasionallydepartingfromthisorder，forthesakeofgeographicalsimplicity。
Theelevationofthelandwithintherecentperiod，andthemodificationsofitssurfacethroughtheactionofthesea(towhichsubjectsIpaidparticularattention)willbefirstdiscussed;Iwillthenpassontothetertiarydeposits，andafterwardstotheolderrocks。Onlythosedistrictsandsectionswillbedescribedindetailwhichappeartometodeservesomeparticularattention;andIwill，attheendofeachchapter，giveasummaryoftheresults。Wewillcommencewiththeproofsoftheupheavaloftheeasterncoastofthecontinent，fromtheRioPlatasouthward;and，intheSecondChapter，followupthesamesubjectalongtheshoresofChileandPeru。
OnthenorthernbankofthegreatestuaryoftheRioPlata，nearMaldonado，Ifoundattheheadofalake，sometimesbrackishbutgenerallycontainingfreshwater，abedofmuddyclay，sixfeetinthickness，withnumerousshellsofspeciesstillexistinginthePlata，namely，theAzaralabiata，d’Orbigny，fragmentsofMytiluseduliformis，d’Orbigny，PaludestrinaIsabellei，d’Orbigny，andtheSolenCaribaeus，Lam。whichlastwasembeddedverticallyinthepositioninwhichithadlived。Theseshellslieattheheightofonlytwofeetabovethelake，norwouldtheyhavebeenworthmentioning，exceptinconnectionwithanalogousfacts。
AtMonteVideo，Inoticednearthetown，andalongthebaseofthemount，bedsofalivingMytilus，raisedsomefeetabovethesurfaceofthePlata：
inasimilarbed，ataheightfromthirteentosixteenfeet，M。Isabellecollectedeightspecies，which，accordingtoM。d’Orbigny，nowliveatthemouthoftheestuary。(“Voyagedansl’AmeriqueMerid。：Part。Geolog。”page21。)AtColoniadelSacramiento，furtherwestward，Iobservedattheheightofaboutfifteenfeetabovetheriver，thereofquitefreshwater，asmallbedofthesameMytilus，whichlivesinbrackishwateratMonteVideo。NearthemouthofUruguay，andforatleastthirty-fivemilesnorthward，thereareatintervalslargesandytracts，extendingseveralmilesfromthebanksoftheriver，butnotraisedmuchaboveitslevel，aboundingwithsmallbivalves，whichoccurinsuchnumbersthatattheAgraciadotheyaresiftedandburntforlime。ThosewhichIexaminedneartheA。S。Juanweremuchworn：theyconsistedofMactraIsabellei，d’Orbigny，mingledwithfewofVenussinuosa，Lam。bothinhabiting，asIaminformedbyM。d’Orbigny，brackishwateratthemouthofthePlata，nearlyorquiteassaltastheopensea。Theloosesand，inwhichtheseshellsarepacked，isheapedintolow，straight，longlinesofdunes，likethoseleftbytheseaattheheadofmanybays。M。d’Orbignyhasdescribedananalogousphenomenononagreaterscale，nearSanPedroontheriverParana，wherehefoundwidelyextendedbedsandhillocksofsand，withvastnumbersoftheAzaralabiata，attheheightofnearly100feet(English)abovethesurfaceofthatriver。
(Ibidpage43。)TheAzarainhabitsbrackishwater，andisnotknowntobefoundnearertoSanPedrothanBuenosAyres，distantaboveahundredmilesinastraightline。NearerBuenosAyres，ontheroadfromthatplacetoSanIsidro，thereareextensivebeds，asIaminformedbySirWoodbineParish，oftheAzaralabiata，lyingataboutfortyfeetabovetheleveloftheriver，anddistantbetweentwoandthreemilesfromit。(“BuenosAyres“
etc。bySirWoodbineParishpage168。)Theseshellsarealwaysfoundonthehighestbanksinthedistrict：theyareembeddedinastratifiedearthymass，preciselylikethatofthegreatPampeandeposithereaftertobedescribed。Inonecollectionoftheseshells，thereweresomevalvesoftheVenussinuosa，Lam。thesamespeciesfoundwiththeMactraonthebanksoftheUruguay。SouthofBuenosAyres，nearEnsenada，thereareotherbedsoftheAzara，someofwhichseemtohavebeenembeddedinyellowish，calcareous，semi-crystallinematter;andSirW。ParishhasgivenmefromthebanksoftheArroyodelTristan，situatedinthissameneighbourhood，atthedistanceofaboutaleaguefromthePlata，aspecimenofapale-
reddish，calcereo-argillaceousstone(preciselylikepartsofthePampeandeposittheimportanceofwhichfactwillbereferredtoinasucceedingchapter)，aboundingwithshellsofanAzara，muchworn，butwhichingeneralformandappearancecloselyresemble，andareprobablyidenticalwith，theA。labiata。Besidestheseshells，cellular，highlycrystallinerock，formedofthecastsofsmallbivalves，isfoundnearEnsenada;andlikewisebedsofsea-shells，whichfromtheirappearanceappeartohavelainonthesurface。SirW。Parishhasgivenmesomeoftheseshells，andM。d’Orbignypronouncesthemtobe：——
1。Buccinanopsglobulosum，d’Orbigny。
2。Olivancillariaauricularia，d’Orbigny。
3。Venusflexuosa，Lam。
4。Cytheraea(imperfect)。
5。MactraIsabellei，d’Orbigny。
6。Ostreapulchella，d’Orbigny。
Besidesthese，SirW。Parishprocured(“BuenosAyres“etc。bySirW。Parishpage168。)(asnamedbyMr。G。B。Sowerby)thefollowingshells：——
7。Volutacolocynthis。
8。Volutaangulata。
9。Buccinum(notspec。？)。
Allthesespecies(with，perhaps，theexceptionofthelast)arerecent，andliveontheSouthAmericancoast。Theseshell-bedsextendfromoneleaguetosixleaguesfromthePlata，andmustliemanyfeetaboveitslevel。Iheard，also，ofbedsofshellsontheSomborombon，andontheRioSalado，atwhichlatterplace，asM。d’Orbignyinformsme，theMactraIsabelleiandVenussinuosaarefound。
DuringtheelevationoftheProvincesofLaPlata，thewatersoftheancientestuaryhavebutlittleaffected(withtheexceptionofthesand-
hillsonthebanksoftheParanaandUruguay)theoutlineoftheland。M。
Parchappe，however，hasdescribedgroupsofsanddunesscatteredoverthewideextentofthePampassouthwardofBuenosAyres(D’Orbigny“VoyageGeolog。”page44。)，whichM。d’Orbignyattributeswithmuchprobabilitytotheactionofthesea，beforetheplainswereraisedaboveitslevel。
(BeforeproceedingtothedistrictssouthwardofLaPlata，itmaybeworthwhilejusttostate，thatthereissomeevidencethatthecoastofBrazilhasparticipatedinasmallamountofelevation。Mr。Burchellinformsme，thathecollectedatSantos(latitude24degreesS。)oyster-shells，apparentlyrecent，somemilesfromtheshore，andquiteabovethetidalaction。WestwardofRiodeJaneiro，CaptainElliotisasserted(seeHarlan“Med。andPhys。Res。”page35andDr。Meigsin“TransactionsoftheAmericanPhilosophicalSociety“)，tohavefoundhumanbones，encrustedwithsea-shells，betweenfifteenandtwentyfeetabovethelevelofthesea。
BetweenRiodeJaneiroandCapeFrioIcrossedsandytractsaboundingwithsea-shells，atadistanceofaleaguefromthecoast;butwhetherthesetractshavebeenformedbyupheaval，orthroughthemereaccumulationofdriftsand，Iamnotpreparedtoassert。AtBahia(latitude13degreesS。)，insomepartsnearthecoast，therearetracesofsea-actionattheheightofabouttwentyfeetaboveitspresentlevel;therearealso，inmanyparts，remnantsofbedsofsandstoneandconglomeratewithnumerousrecentshells，raisedalittleabovethesea-level。Imayadd，thatattheheadofBahiaBaythereisaformation，aboutfortyfeetinthickness，containingtertiaryshellsapparentlyoffresh-waterorigin，nowwashedbytheseaandencrustedwithBalini;thisappearstoindicateasmallamountofsubsidencesubsequenttoitsdeposition。AtPernambuco(latitude8degreesS。)，inthealluvialortertiarycliffs，surroundingthelowlandonwhichthecitystands，Ilookedinvainfororganicremains，orotherevidenceofchangesinlevel。)
SOUTHWARDOFTHEPLATA。
ThecoastasfarasBahiaBlanca(inlatitude39degreesS。)isformedeitherofahorizontalrangeofcliffs，orofimmenseaccumulationsofsand-dunes。WithinBahiaBlanca，asmallpieceoftableland，abouttwentyfeetabovehigh-watermark，calledPuntaAlta，isformedofstrataofcementedgravelandofredearthymud，aboundingwithshells(withotherslyinglooseonthesurface)，andthebonesofextinctmammifers。Theseshells，twentyinnumber，togetherwithaBalanusandtwocorals，areallrecentspecies，stillinhabitingtheneighbouringseas。TheywillbeenumeratedintheFourthChapter，whendescribingthePampeanformation;
fiveofthemareidenticalwiththeupraisedonesfromnearBuenosAyres。
ThenorthernshoreofBahiaBlancais，inmainpart，formedofimmensesand-dunes，restingongravelwithrecentshells，andranginginlinesparalleltotheshore。Theserangesareseparatedfromeachotherbyflatspaces，composedofstiffimpureredclay，inwhich，atthedistanceofabouttwomilesfromthecoast，Ifoundbydiggingafewminutefragmentsofsea-shells。Thesand-dunesextendseveralmilesinland，andstandonaplain，whichslopesuptoaheightofbetweenonehundredandtwohundredfeet。Numerous，small，well-roundedpebblesofpumiceliescatteredbothontheplainandsand-hillocks：atMonteHermoso，ontheflatsummitofacliff，Ifoundmanyofthemataheightof120feet(angularmeasurement)
abovethelevelofthesea。Thesepumicepebbles，nodoubt，wereoriginallybroughtdownfromtheCordillerabytheriverswhichcrossthecontinent，inthesamewayastheriverNegroancientlybroughtdown，andstillbringsdown，pumice，andastheriverChupatbringsdownscoriae：whenoncedeliveredatthemouthofariver，theywouldnaturallyhavetravelledalongthecoasts，andbeencastupduringtheelevationoftheland，atdifferentheights。Theoriginoftheargillaceousflats，whichseparatetheparallelrangesofsand-dunes，seemsduetothetidesherehavingatendency(asIbelievetheyhaveonmostshoal，protectedcoasts)tothrowupabarparalleltotheshore，andatsomedistancefromit;thisbargraduallybecomeslarger，affordingabasefortheaccumulationofsand-
dunes，andtheshallowspacewithinthenbecomessiltedupwithmud。Therepetitionofthisprocess，withoutanyelevationoftheland，wouldformalevelplaintraversedbyparallellinesofsand-hillocks;duringaslowelevationoftheland，thehillockswouldrestonagentlyinclinedsurface，likethatonthenorthernshoreofBahiaBlanca。Ididnotobserveanyshellsinthisneighbourhoodatagreaterheightthantwentyfeet;andthereforetheageofthesea-driftedpebblesofpumice，nowstandingattheheightof120feet，mustremainuncertain。
ThemainplainsurroundingBahiaBlancaIestimatedatfromtwohundredtothreehundredfeet;itinsensiblyrisestowardsthedistantSierraVentana。
Thereareinthisneighbourhoodsomeotherandlowerplains，buttheydonotabutoneatthefootoftheother，inthemannerhereaftertobedescribed，socharacteristicofPatagonia。Theplainonwhichthesettlementstandsiscrossedbymanylowsand-dunes，aboundingwiththeminuteshellsofthePaludestrinaaustralis，d’Orbigny，whichnowlivesinthebay。Thislowplainisboundedtothesouth，attheCabezadelBuey，bythecliff-formedmarginofawideplainofthePampeanformation，whichI
estimatedatsixtyfeetinheight。Onthesummitofthiscliffthereisarangeofhighsand-dunesextendingseveralmilesinaneastandwestline。
SouthwardofBahiaBlanca，theriverColoradoflowsbetweentwoplains，apparentlyfromthirtytofortyfeetinheight。Oftheseplains，thesouthernoneslopesuptothefootofthegreatsandstoneplateauoftheRioNegro;andthenorthernoneagainstanescarpmentofthePampeandeposit;sothattheColoradoflowsinavalleyfiftymilesinwidth，betweentheupperescarpments。Istatethis，becauseonthelowplainatthefootofthenorthernescarpment，Icrossedanimmenseaccumulationofhighsand-dunes，estimatedbytheGauchosatnolessthaneightmilesinbreadth。Thesedunesrangewestwardfromthecoast，whichistwentymilesdistant，tofarinland，inlinesparalleltothevalley;theyareseparatedfromeachotherbyargillaceousflats，preciselylikethoseonthenorthernshoreofBahiaBlanca。Atpresentthereisnosourcewhencethisimmenseaccumulationofsandcouldproceed;butif，asIbelieve，theupperescarpmentsonceformedtheshoresofanestuary，inthatcasethesandstoneformationoftheriverNegrowouldhaveaffordedaninexhaustiblesupplyofsand，whichwouldnaturallyhaveaccumulatedonthenorthernshore，asoneverypartofthecoastopentothesouthwindsbetweenBahiaBlancaandBuenosAyres。
AtSanBlas(40degrees40’S。)alittlesouthofthemouthoftheColorado，M。d’Orbignyfoundfourteenspeciesofexistingshells(sixofthemidenticalwiththosefromBahiaBlanca)，embeddedintheirnaturalpositions。(“Voyage“etc。page54。)Fromthezoneofdepthwhichtheseshellsareknowntoinhabit，theymusthavebeenupliftedthirty-twofeet。
Healsofound，atfromfifteentotwentyfeetabovethisbed，theremainsofanancientbeach。
Tenmilessouthward，but120milestothewest，atPortS。Antonio，theOfficersemployedontheSurveyassuredmethattheysawmanyoldsea-
shellsstrewedonthesurfaceoftheground，similartothosefoundonotherpartsofthecoastofPatagonia。AtSanJosef，ninetymilessouthinnearlythesamelongitude，Ifound，abovethegravel，whichcapsanoldtertiaryformation，anirregularbedandhillockofsand，severalfeetinthickness，aboundingwithshellsofPatelladeaurita，MytilusMagellanicus，thelatterretainingmuchofitscolour;FususMagellanicus(andavarietyofthesame)，andalargeBalanus(probablyB。Tulipa)，allnowfoundonthiscoast：Iestimatedthisbedatfromeightytoonehundredfeetabovethelevelofthesea。Tothewestwardofthisbay，thereisaplainestimatedatbetweentwohundredandthreehundredfeetinheight：thisplainseems，frommanymeasurements，tobeacontinuationofthesandstoneplatformoftheriverNegro。Thenextplacesouthward，whereIlanded，wasatPortDesire，340milesdistant;butfromtheintermediatedistrictsI
received，throughthekindnessoftheOfficersoftheSurvey，especiallyfromLieutenantStokesandMr。King，manyspecimensandsketches，quitesufficienttoshowthegeneraluniformityofthewholelineofcoast。Imayherestate，thatthewholeofPatagoniaconsistsofatertiaryformation，restingonandsometimessurroundinghillsofporphyryandquartz：thesurfaceiswornintomanywidevalleysandintolevelstep-formedplains，risingoneaboveanother，allcappedbyirregularbedsofgravel，chieflycomposedofporphyriticrocks。Thisgravelformationwillbeseparatelydescribedattheendofthechapter。
Myobjectingivingthefollowingmeasurementsoftheplains，astakenbytheOfficersoftheSurvey，is，aswillhereafterbeseen，toshowtheremarkableequabilityoftherecentelevatorymovements。RoundthesouthernpartsofNuevoGulf，asfarastheRiverChupat(seventymilessouthwardofSanJosef)，thereappeartobeseveralplains，ofwhichthebestdefinedarehererepresented。
(InthefollowingDiagrams：
1。BaselineisLevelofsea。
2。Scaleis1/20ofinchto100feetvertical。
3。Heightisshowninfeetthus：
An。M。alwaysstandsforangularortrigonometricalmeasurement。
Ba。M。alwaysstandsforbarometricalmeasurement。
Est。alwaysstandsforestimationbytheOfficersoftheSurvey。
DIAGRAM1。SECTIONOFSTEP-FORMEDPLAINSSOUTHOFNUEVOGULF。
>FromEast(sealevel)toWest(high)：
Terrace1。80Est。
Terrace2。200-220An。M。
Terrace3。350An。M。)
Theupperplainisherewelldefined(calledTableHills);itsedgeformsaclifforlineofescarpmentmanymilesinlength，projectingoveralowerplain。ThelowestplaincorrespondswiththatatSanJosefwiththerecentshellsonitssurface。Betweenthislowestandtheuppermostplain，thereisprobablymorethanonestep-formedterrace：severalmeasurementsshowtheexistenceoftheintermediateoneoftheheightgiveninDiagram1。
(DIAGRAM2。SECTIONOFPLAINSINTHEBAYOFST。GEORGE。
>FromEast(sealevel)toWest(high)：
Terrace1。250An。M。
Terrace2。330An。M。
Terrace3。580An。M。
Terraces4，5and6notmeasured。
Terrace7。1，200Est。)
NearthenorthheadlandofthegreatBayofSt。George(100milessouthoftheChupat)，twowell-markedplainsof250and330feetweremeasured：
thesearesaidtosweeproundagreatpartoftheBay。Atitssouthheadland，120milesdistantfromthenorthheadland，the250feetplainwasagainmeasured。Inthemiddleofthebay，ahigherplainwasfoundattwoneighbouringplaces(TilliRoadsandC。Marques)tobe580feetinheight。
Abovethisplain，towardstheinterior，Mr。Stokesinformsmethattherewereseveralotherstep-formedplains，thehighestofwhichwasestimatedat1，200feet，andwasseenrangingatapparentlythesameheightfor150
milesnorthward。Alltheseplainshavebeenwornintogreatvalleysandmuchdenuded。Thesectionin，Diagram3isillustrativeofthegeneralstructureofthegreatBayofSt。George。AtthesouthheadlandoftheBayofSt。George(nearC。ThreePoints)the250plainisveryextensive。
(DIAGRAM3。SECTIONOFPLAINSATPORTDESIRE。
>FromEast(sealevel)toWest(high)：
Terrace1。100Est。
Terrace2。245-255Ba。M。Shellsonsurface。
Terrace3。330Ba。M。Shellsonsurface。
Terrace4。Notmeasured。)
AtPortDesire(fortymilessouthward)Imadeseveralmeasurementswiththebarometerofaplain，whichextendsalongthenorthsideoftheportandalongtheopencoast，andwhichvariesfrom245to255feetinheight：thisplainabutsagainstthefootofahigherplainof330feet，whichextendsalsofarnorthwardalongthecoast，andlikewiseintotheinterior。Inthedistanceahigherinlandplatformwasseen，ofwhichIdonotknowtheheight。Inthreeseparateplaces，Iobservedthecliffofthe245-255feetplain，fringedbyaterraceornarrowplainestimatedataboutonehundredfeetinheight。TheseplainsarerepresentedinthesectionDiagram3。
Inmanyplaces，evenatthedistanceofthreeandfourmilesfromthecoast，Ifoundonthegravel-cappedsurfaceofthe245-255feet，andofthe330feetplain，shellsofMytilusMagellanicus，M。edulis，Patelladeaurita，andanotherPatella，toomuchworntobeidentified，butapparentlysimilartoonefoundabundantlyadheringtotheleavesofthekelp。Thesespeciesarethecommonestnowlivingonthiscoast。Theshellsallappearedveryold;theblueofthemusselswasmuchfaded;andonlytracesofcolourcouldbeperceivedinthePatellas，ofwhichtheoutersurfaceswerescalingoff。Theylayscatteredonthesmoothsurfaceofthegravel，butaboundedmostincertainpatches，especiallyattheheadsofthesmallervalleys：theygenerallycontainedsandintheirinsides;andI
presumethattheyhavebeenwashedbyalluvialactionoutofthinsandylayers，tracesofwhichmaysometimesbeseencoveringthegravel。Theseveralplainshaveverylevelsurfaces;butallarescoopedoutbynumerousbroad，winding，flat-bottomedvalleys，inwhich，judgingfromthebushes，streamsneverflow。Theseremarksonthestateoftheshells，andonthenatureoftheplains，applytothefollowingcases，soneednotberepeated。
(DIAGRAM4。SECTIONOFPLAINSATPORTS。JULIAN。
>FromEast(sealevel)toWest(high)：
Terrace1。Shellsonsurface。90Est。
Terrace2。430An。M。
Terrace3。560An。M。
Terrace4。950An。M。)
SouthwardofPortDesire，theplainshavebeengreatlydenuded，withonlysmallpiecesoftablelandmarkingtheirformerextension。ButoppositeBirdIsland，twoconsiderablestep-formedplainsweremeasured，andfoundrespectivelytobe350and590feetinheight。ThislatterplainextendsalongthecoastclosetoPortSt。Julian(110milessouthofPortDesire);
seeDiagram4。
Thelowestplainwasestimatedatninetyfeet：itisremarkablefromtheusualgravel-bedbeingdeeplywornintohollows，whicharefilledupwith，aswellasthegeneralsurfacecoveredby，sandyandreddishearthymatter：
inoneofthehollowsthusfilledup，theskeletonoftheMacraucheniaPatachonica，aswillhereafterbedescribed，wasembedded。Onthesurfaceandintheupperpartsofthisearthymass，therewerenumerousshellsofMytilusMagellanicusandM。edulis，Patelladeaurita，andfragmentsofotherspecies。Thisplainistolerablylevel，butnotextensive;itformsapromontorysevenoreightmileslong，andthreeorfourwide。TheupperplainsinDiagram4weremeasuredbytheOfficersoftheSurvey;theywereallcappedbythickbedsofgravel，andwereallmoreorlessdenuded;the950plainconsistsmerelyofseparate，truncated，gravel-cappedhills，twoofwhich，bymeasurement，werefoundtodifferonlythreefeet。The430
feetplainextends，apparentlywithhardlyabreak，tonearthenorthernentranceoftheRioSantaCruz(fiftymilestothesouth);butitwastherefoundtobeonly330feetinheight。
(DIAGRAM5。SECTIONOFPLAINSATTHEMOUTHOFTHERIOSANTACRUZ。
>FromEast(sealevel)toWest(high)：
Terrace1。(sloping)355Ba。M。Shellsonsurface。463Ba。M。
Terrace2。710An。M。
Terrace3。840An。M。)
OnthesouthernsideofthemouthoftheSantaCruzwehaveDiagram5，whichIamabletogivewithmoredetailthanintheforegoingcases。
Theplainmarked355feet(asascertainedbythebarometerandbyangularmeasurement)isacontinuationoftheabove-mentioned330feetplain：itextendsinaN。W。directionalongthesouthernshoresoftheestuary。Itiscappedbygravel，whichinmostpartsiscoveredbyathinbedofsandyearth，andisscoopedoutbymanyflat-bottomedvalleys。Itappearstotheeyequitelevel，butinproceedinginaS。S。W。course，towardsanescarpmentdistantaboutsixmiles，andlikewiserangingacrossthecountryinaN。W。line，itwasfoundtoriseatfirstinsensibly，andthenforthelasthalf-mile，sensibly，closeuptothebaseoftheescarpment：atthispointitwas463feetinheight，showingariseof108feetinthesixmiles。Onthis355-463feetplain，IfoundseveralshellsofMytilusMagellanicusandofaMytilus，whichMr。Sowerbyinformsmeisyetunnamed，thoughwell-knownasrecentonthiscoast;Patelladeaurita;Fusus，I
believe，Magellanicus，butthespecimenhasbeenlost;andatthedistanceoffourmilesfromthecoast，attheheightofaboutfourhundredfeet，therewerefragmentsofthesamePatellaandofaVoluta(apparentlyV。
ancilla)partiallyembeddedinthesuperficialsandyearth。Alltheseshellshadthesameancientappearancewiththosefromtheforegoinglocalities。AsthetidesalongthispartofthecoastriseattheSyzygalperiodfortyfeet，andthereforeformawell-markedbeach-line，I
particularlylookedoutforridgesincrossingthisplain，which，aswehaveseen，rises108feetinaboutsixmiles，butIcouldnotseeanytracesofsuch。Thenexthighestplainis710feetabovethesea;itisverynarrow，butlevel，andiscappedwithgravel;itabutstothefootofthe840feetplain。Thissummit-plainextendsasfarastheeyecanrange，bothinlandalongthesouthernsideofthevalleyoftheSantaCruz，andsouthwardalongtheAtlantic。
THEVALLEYOFTHER。SANTACRUZ。
ThisvalleyrunsinaneastandwestdirectiontotheCordillera，adistanceofaboutonehundredandsixtymiles。ItcutsthroughthegreatPatagoniantertiaryformation，including，intheupperhalfofthevalley，immensestreamsofbasalticlava，whichaswellasthesofterbeds，arecappedbygravel;andthisgravel，highuptheriver，isassociatedwithavastboulderformation。(Ihavedescribedthisformationinapaperinthe“GeologicalTransactions“volume6page415。)Inascendingthevalley，theplainwhichatthemouthonthesouthernsideis355feethigh，isseentotrendtowardsthecorrespondingplainonthenorthernside，sothattheirescarpmentsappearliketheshoresofaformerestuary，largerthantheexistingone：theescarpments，also，ofthe840feetsummit-plain(withacorrespondingnorthernone，whichismetwithsomewayupthevalley)，appearliketheshoresofastilllargerestuary。Fartherupthevalley，thesidesareboundedthroughoutitsentirelengthbylevel，gravel-cappedterraces，risingaboveeachotherinsteps。Thewidthbetweentheupperescarpmentsisonanaveragebetweensevenandtenmiles;inonespot，however，wherecuttingthroughthebasalticlava，itwasonlyonemileandahalf。Betweentheescarpmentsofthesecondhighestterracetheaveragewidthisaboutfourorfivemiles。Thebottomofthevalley，atthedistanceof110milesfromitsmouth，beginssensiblytoexpand，andsoonformsaconsiderableplain，440feetabovethelevelofthesea，throughwhichtheriverflowsinagutfromtwentytofortyfeetindepth。Iherefound，atapoint140milesfromtheAtlantic，andseventymilesfromthenearestcreekofthePacific，attheheightof410feet，averyoldandwornshellofPatelladeaurita。Lowerdownthevalley，105milesfromtheAtlantic(longitude71degreesW。)，andatanelevationofabout300feet，Ialsofound，inthebedoftheriver，twomuchwornandbrokenshellsoftheVolutaancilla，stillretainingtracesoftheircolours;andoneofthePatelladeaurita。Itappearedthattheseshellshadbeenwashedfromthebanksintotheriver;consideringthedistancefromthesea，thedesertandabsolutelyunfrequentedcharacterofthecountry，andtheveryancientappearanceoftheshells(exactlylikethosefoundontheplainsnearerthecoast)，thereis，Ithink，nocausetosuspectthattheycouldhavebeenbroughtherebyIndians。
Theplainattheheadofthevalleyistolerablylevel，butwater-worn，andwithmanysand-dunesonitlikethoseonasea-coast。Atthehighestpointtowhichweascended，itwassixteenmileswideinanorthandsouthline;
andforty-fivemilesinlengthinaneastandwestline。Itisborderedbytheescarpments，oneabovetheother，oftwoplains，whichdivergeastheyapproachtheCordillera，andconsequentlyresemble，attwolevels，theshoresofgreatbaysfacingthemountains;andthesemountainsarebreachedinfrontofthelowerplainbyaremarkablegap。Thevalley，therefore，oftheSantaCruzconsistsofastraightbroadcut，aboutninetymilesinlength，borderedbygravel-cappedterracesandplains，theescarpmentsofwhichatbothendsdivergeorexpand，oneovertheother，afterthemanneroftheshoresofgreatbays。Bearinginmindthispeculiarformoftheland——thesand-dunesontheplainattheheadofthevalley——thegapintheCordillera，infrontofit——thepresenceintwoplacesofveryancientshellsofexistingspecies——andlastly，thecircumstanceofthe355-453
feetplain，withthenumerousmarineremainsonitssurface，sweepingfromtheAtlanticcoast，farupthevalley，Ithinkwemustadmit，thatwithintherecentperiod，thecourseoftheSantaCruzformedasea-straitintersectingthecontinent。Atthisperiod，thesouthernpartofSouthAmericaconsistedofanarchipelagoofislands360milesinanorthandsouthline。Weshallpresentlysee，thattwootherstraitsalso，sinceclosed，thencutthroughTierradelFuego;Imayadd，thatoneofthemmustatthattimehaveexpandedatthefootoftheCordilleraintoagreatbay(nowOtwayWater)likethatwhichformerlycoveredthe440feetplainattheheadoftheSantaCruz。
(DIAGRAM6。NORTHANDSOUTHSECTIONACROSSTHETERRACESBOUNDINGTHEVALLEY
OFTHERIVERSANTACRUZ，HIGHUPITSCOURSE。
Theheightofeachterrace，abovetheleveloftheriver(furthesttonearesttotheriver)infeet：
A，northandsouth：1，122
B，northandsouth：869
C，northandsouth：639
D，north：notmeasured。D，north？(suggestsouth)：185
E：20
BedofRiver。
Verticalscale1/20ofinchto100feet;butterraceE，beingonlytwentyfeetabovetheriver，hasnecessarilybeenraised。Thehorizontaldistancesmuchcontracted;thedistancefromtheedgeofANorthtoASouthbeingonanaveragefromseventotenmiles。)
Ihavesaidthatthevalleyinitswholecourseisborderedbygravel-
cappedplains。Thesection(Diagram6)，supposedtobedrawninanorthandsouthlineacrossthevalley，canscarcelybeconsideredasmorethanillustrative;forduringourhurriedascentitwasimpossibletomeasurealltheplainsatanyoneplace。AtapointnearlymidwaybetweentheCordilleraandtheAtlantic，Ifoundtheplain(Anorth)1，122feetabovetheriver;allthelowerplainsonthissidewerehereunitedintoonegreatbrokencliff：atapointsixteenmileslowerdownthestream，IfoundbymeasurementandestimationthatB(north)was869abovetheriver：veryneartowhereA(north)wasmeasured，C(north)was639abovethesamelevel：theterraceD(north)wasnowheremeasured：thelowestE(north)wasinmanyplacesabouttwentyfeetabovetheriver。Theseplainsorterraceswerebestdevelopedwherethevalleywaswidest;thewholefive，likegiganticsteps，occurredtogetheronlyatafewpoints。Thelowerterracesarelesscontinuousthanthehigherones，andappeartobeentirelylostintheupperthirdofthevalley。TerraceC(south)，howeverwastracedcontinuouslyforagreatdistance。TheterraceB(north)，atapointfifty-
fivemilesfromthemouthoftheriver，wasfourmilesinwidth;higherupthevalleythisterrace(oratleastthesecondhighestone，forIcouldnotalwaystraceitcontinuously)wasabouteightmileswide。Thissecondplainwasgenerallywiderthanthelowerones——asindeedfollowsfromthevalleyfromA(north)toA(south)beinggenerallynearlydoublethewidthoffromB(north)toB(south)。Lowdownthevalley，thesummit-plainA
(south)iscontinuouswiththe840feetplainonthecoast，butitissoonlostoruniteswiththeescarpmentofB(south)。ThecorrespondingplainA
(north)，onthenorthsideofthevalley，appearstorangecontinuouslyfromtheCordilleratotheheadofthepresentestuaryoftheSantaCruz，whereittrendsnorthwardtowardsPortSt。Julian。NeartheCordillerathesummit-plainonbothsidesofthevalleyisbetween3，200and3，300feetinheight;at100milesfromtheAtlantic，itis1，416feet，andonthecoast840feet，allabovethesea-beach;sothatinadistanceof100milestheplainrises576feet，andmuchmorerapidlyneartotheCordillera。ThelowerterracesBandCalsoappeartoriseastheyrunupthevalley;thusD(north)，measuredattwopointstwenty-fourmilesapart，wasfoundtohaverisen185feet。FromseveralreasonsIsuspect，thatthisgradualinclinationoftheplainsupthevalley，hasbeenchieflycausedbytheelevationofthecontinentinmass，havingbeenthegreaterthenearertotheCordillera。
Alltheterracesarecappedwithwell-roundedgravel，whichrestseitheronthedenudedandsometimesfurrowedsurfaceofthesofttertiarydeposits，oronthebasalticlava。Thedifferenceinheightbetweensomeofthelowerstepsorterracesseemstobeentirelyowingtoadifferenceinthethicknessofthecappinggravel。Furrowsandinequalitiesinthegravel，wheresuchoccur，arefilledupandsmoothedoverwithsandyearth。Thepebbles，especiallyonthehigherplains，areoftenwhitewashed，andevencementedtogetherbyawhitealuminoussubstance，andIoccasionallyfoundthistobethecasewiththegravelontheterraceD。Icouldnotperceiveanytraceofasimilardepositiononthepebblesnowthrownupbytheriver，andthereforeIdonotthinkthatterraceDwasriver-formed。AstheterraceEgenerallystandsabouttwentyfeetabovethebedoftheriver，myfirstimpressionwastodoubtwhethereventhislowestonecouldhavebeensoformed;butitshouldalwaysbeborneinmind，thatthehorizontalupheavalofadistrict，byincreasingthetotaldescentofthestreams，willalwaystendtoincrease，firstnearthesea-coastandthenfurtherandfurtherupthevalley，theircorrodinganddeepeningpowers：sothatanalluvialplain，formedalmostonalevelwithastream，will，afteranelevationofthiskind，intimebecutthrough，andleftstandingataheightneveragaintobereachedbythewater。WithrespecttothethreeupperterracesoftheSantaCruz，Ithinktherecanbenodoubt，thattheyweremodelledbythesea，whenthevalleywasoccupiedbyastrait，inthesamemanner(hereaftertobediscussed)asthegreaterstep-formed，shell-
strewedplainsalongthecoastofPatagonia。
ToreturntotheshoresoftheAtlantic：the840feetplain，atthemouthoftheSantaCruz，isseenextendinghorizontallyfartothesouth;andI
aminformedbytheOfficersoftheSurvey，thatbendingroundtheheadofCoyInlet(sixty-fivemilessouthward)，ittrendsinland。Outliersofapparentlythesameheightareseenfortymilesfarthersouth，inlandoftheriverGallegos;andaplaincomesdowntoCapeGregory(thirty-fivemilessouthward)，intheStraitofMagellan，whichwasestimatedatbetweeneighthundredandonethousandfeetinheight，andwhich，risingtowardstheinterior，iscappedbytheboulderformation。SouthoftheStraitofMagellan，therearelargeoutlyingmassesofapparentlythesamegreattableland，extendingatintervalsalongtheeasterncoastofTierradelFuego：attwoplaceshere，110milesapart，thisplainwasfoundtobe950
and970feetinheight。
